Radioactivity in the natural world

from 26. May 2020
A new part of the permanent exhibition in Hall 4 focuses on radioactivity – from natural radioactivity to geological nuclear reactors and minerals that glow in the dark.
Natural radioactivity
Radioactivity often gets a bad press. Many people think that radioactivity is always artificial, but in fact it is a part of our natural environment – man-made radioactivity only accounts for around a third of all radioactivity that we are exposed to. Therefore, two thirds come from nature, most as a result of decaying natural radioactive substances and from cosmic radiation. Radioactivity itself was only discovered by chance. In 1896, during research on the fluorescence of natural minerals, Henri Becquerel made a mistake in an experiment and ended up finding a previously unknown type of radiation in uranium-rich materials.
 
Radioactivity includes various types of radiation – for example, helium nuclei occur as alpha radiation, electrons as beta radiation, and electromagnetic radiation as gamma radiation. These are released during the decay of naturally occurring unstable isotopes, which have formed, for example, in the interior of stars. Energy-rich cosmic radiation comes not only from the Sun, but also from distant galaxies. By interacting with Earth's atmosphere, this cosmic radiation results in additional particles that constantly penetrate the human body.
A special detector in the exhibition shows "live" images of this cosmic radiation.

Witness of a supernova explosion: Manganese nodule from the depths of the Pacific Ocean
 
The intensity of cosmic radiation on Earth varies. It can change if, for example, a supernova explodes near our solar system. In that case, radioactive isotopes such as iron-60 can rain down on Earth. Such radioactive markers can still be found today, for example in manganese nodules on the ocean floor. Such a manganese nodule is shown in one of the new display cases (permanent loan of the Free University of Berlin) - it contains a thin, weakly radioactive layer resulting from a supernova explosion which happened around two million years ago.
 
Geological power station
Just over two billion years ago, in Oklo in Gabon (West-Central Africa), environmental conditions were perfect for natural chain reactions in uranium ores. For many millions of years, nuclear fission in uranium generated energy in 19 known "reactor cores". Today this radiation has almost completely decayed, so a (very rare) rock sample from Oklo can be shown here in the museum.
 
Minerals that glow in the dark
This newly re-designed display case shows a selection of minerals which glow when exposed to short or long wavelength UV radiation. If you look closely you will even be able to see phosphorescence.
 
Materials become photo-luminescent when exposed to energy-rich UV radiation. If the glowing effect happens directly under the UV lamp, this is known as fluorescence. If the mineral continues to glow even after the UV lamp has been switched off, this is called phosphorescence. Fluorescent minerals can convert UV radiation invisible to the human eye into light we are able to see.
 
This glowing effect was first observed in 1852 by the British physicist George Stokes with the mineral fluorite.
 
The most common triggers for photo-luminescence are certain metal ions. These include manganese, chromium, rare earth elements, copper, tin, tungsten, lead, and uranium. The most impressive fluorescent minerals come from the zinc deposit in Franklin, New Jersey, USA. Fluorescent minerals can also be found in Austria, for example, the tungsten ore scheelite.

Exhibition opening on May, 26, 2020:
UV display
                                 case with fluorescing minerals
Metatyuyamunite (yellow) with malachite (green)
Oklo specimen: Core from a natural nuclear reactor
  
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